writer-json-sarif: encode per-warning CWE property

... so that the data is processed by DefectDojo

Fixes: #125
Closes: #126

Author: kdudka

src/lib/writer-json-sarif.cc

@@ -276,10 +276,15 @@ void SarifTreeEncoder::appendDef(const Defect &def)
         shellCheckMap_[ruleId] = sm[2];
     }
 
-    if (def.cwe)
+    if (def.cwe) {
         // update CWE map
         cweMap_[ruleId] = def.cwe;
 
+        // encode per-warning CWE property
+        object cweProp = {{ "cwe", "CWE-" + std::to_string(def.cwe) }};
+        result["properties"] = std::move(cweProp);
+    }
+
     // key event severity level
     sarifEncodeLevel(&result, keyEvt.event);